PET/CT comparing (68)Ga-DOTATATE and other radiopharmaceuticals and in comparison with CT/MRI for the localization of sporadic metastatic pheochromocytoma and paraganglioma

Evaluation of somatostatin, CXCR4 chemokine and endothelin A receptor expression in a large set of paragangliomas

Paragangliomas are predominantly benign tumors, but in some cases invasive growth and also metastasis are observed. Given the limited number of nonsurgical treatment options, novel target structures for diagnostics and therapy of this tumor entity are urgently needed. In the present study, expression of all five somatostatin receptor (SST) subtypes, chemokine receptor CXCR4 and endothelin receptor type A (ETA) was assessed by means of immunohistochemistry in a total of 66 paraffin-embedded paraganglioma samples from 55 patients. The stainings were rated by means of the Immunoreactive Score and correlated to clinical data and to succinate dehydrogenase subunit B (SDHB) expression. SST2A was by far the most prominent receptor in the paragangliomas investigated. It was present in 89% of the tumors at a high intensity, followed by SST5, SST3, SST1 and SST4, which were detected in 47%, 35%, 35% and 13% of the samples, respectively. SDHB positive tumors exhibited significantly higher SST2A and SST3 expression as compared to SDHB negative cases. There was no correlation between SST and Ki-67 expression or grading of the tumors and no difference in SST expression between primary tumors and metastases. Cell surface expression of CXCR4 and ETA was detected only in few samples. On tumor capillaries, however, exceptionally strong staining for these two receptors was noticed in the vast majority of the tumors. In conclusion, paragangliomas are well suited for SST2A-based diagnostics and treatment modalities. An indirect targeting of these highly vascularized tumors via CXCR4 or ETA may also represent a promising future strategy.

Functional Imaging of Paragangliomas with an Emphasis on Von Hippel-Lindau-Associated Disease: A Mini Review

Few reports have presented data and results on functional (i.e., nuclear medicine) imaging of paragangliomas and pheochromocytomas (PGLs/PHEOs) for von Hippel-Lindau (VHL) patients. Nuclear medicine localization modalities for chromaffin tumors can be specific or nonspecific. Specific methods make use of the expression of the human norepinephrine transporter (hNET) and vesicular monoamine transporters (VMATs) by these tumors. These permit the use of radiolabeled ligands that enter the synthesis and storage pathway of catecholamines. Nonspecific methods are not related to the synthesis, uptake, or storage of catecholamines but make use of the tumors' high glucose metabolism or expression of somatostatin receptors. Consensuses and guidelines suggest that metastatic and sporadic PHEOs/PGLs in VHL patients (as in patients with chromaffin tumors of yet unknown genotype) should be evaluated first with ¹⁸F-dihydroxyphenylalanine (¹⁸F-DOPA) positron emission tomography/computed tomography (PET/CT). The functional imaging of second choice is ¹²³I-metaiodobenzylguanidine (¹²³I-MIBG) for PHEOs in VHL patients. ¹²³I-MIBG, ⁶⁸Ga-DOTATATE/DOTATOC/DOTANOC PET/CT, or ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) PET/CT can be a second choice of functional imaging for PGLs in VHL patients.

Adrenal Imaging

Cross-sectional imaging can make a specific diagnosis in lesions, such as myelolipomas, cysts, and hemorrhage, and is often sufficient to distinguish benign from malignant adrenal processes. CT and MRI are useful studies to identify pheochromocytomas and cortisol-secreting or androgen-secreting tumors. In patients with primary aldosteronism, adrenal venous sampling remains the most accurate localizing study and should be performed in all patients older than 35. Radiolabeled isotope studies serve as second-line diagnostic tests for malignant adrenal tumors, primary or metastatic, as well as for pheochromocytoma. Nuclear imaging studies should follow a robust hormonal diagnosis and be correlated with findings on cross-sectional imaging.

Efficacy of Peptide Receptor Radionuclide Therapy for Functional Metastatic Paraganglioma and Pheochromocytoma

PURPOSE

Treatment options for unresectable paraganglioma (PGL)/pheochromocytoma (PCC), especially with uncontrolled secondary hypertension (HTN), are limited. Preliminary studies with peptide receptor radionuclide therapy (PRRT) suggest efficacy, but data on HTN control and survival are lacking. We assessed PRRT outcomes in such patients from two referral centers.

METHODS

Twenty consecutive patients (13 men; age range, 21 to 77 years) with high somatostatin receptor (SSTR) expression treated with 177Lu-DOTA-octreotate, nine with radiosensitizing chemotherapy, were retrospectively reviewed. Median cumulative activity was 22 GBq (median 4 cycles). Fourteen patients were treated for uncontrolled HTN and six for progressive or symptomatic metastatic disease or local recurrence.

RESULTS

Three months after PRRT, 8 of 14 patients treated for HTN required reduced medication doses, 5 had no change in anti-HTN doses, and 1 was lost to follow-up. Eighty-six percent had serum chromogranin-A reduction. Of the entire cohort, 36% had disease regression (29% partial and 7% minor response) on computed tomography, with stable findings in 50%. Three other patients had bony disease evaluable only on SSTR imaging (2 partial response and 1 stable). Median progression-free survival was 39 months; median overall survival was not reached (5 deaths; median follow-up, 28 months). Four patients had grade 3 lymphopenia; 2 had grade 3 thrombocytopenia. Renal impairment in 2 patients was attributed to underlying disease processes.

CONCLUSIONS

PRRT achieves worthwhile clinical and biochemical responses with low toxicity and encouraging survival in PGL/PCC. Because PRRT has logistic and radiation-safety advantages compared to 131I-MIBG therapy, further prospective evaluation is warranted.

Recent advances in the imaging of pheochromocytomas and paragangliomas

Pheochromocytoma and paraganglioma (PPGL) belong to the family of neural crest cell-derived neoplasms, and can be widely distributed throughout the body. Over the past few years, with respect to these tumors, precision medicine has offered the promise of improved patient care. Through tumor visualization and identification of molecular signatures, nuclear medicine is capable of playing a key role in PPGL precision medicine. 68Ga-labeled somatostatin analogs were found to improve the detection and staging of head and neck paragangliomas, SDHx-related PPGLs and metastatic PPGLs regardless of genetic background. For PPGLs associated with increased kinase signaling or HIF2A mutations, 18F-fluorodihydroxyphenylalanine appears to be the most informative radiopharmaceutical. This review emphasizes the current theranostic approaches and future perspective related to PPGL imaging options.

Long-Acting Somatostatin Analog Therapy Differentially Alters 68Ga-DOTATATE Uptake in Normal Tissues Compared with Primary Tumors and Metastatic Lesions

Synthetic somatostatin analogs have been posed as a potential source of error in somatostatin receptor imaging through interference with tumor detection; however, experimental models and clinical studies have shown a complex mechanism of the effect of octreotide on tumors. The aim of this study was to assess whether ⁶⁸Ga-DOTATATE uptake before treatment with long-acting somatostatin analogs differs from that after treatment. Methods: Thirty patients (15 men; age [mean ± SD], 64.6 ± 13.4 y) who had intermediately differentiated to well-differentiated neuroendocrine tumors and who underwent ⁶⁸Ga-DOTATATE PET/CT scanning before and after receiving long-acting repeatable octreotide (Sandostatin LAR) were included in the study. The SUV_max and SUV_mean of healthy target organs, residual primary tumor, and up to 5 lesions with the highest SUV_max in each organ were compared before and after octreotide treatment. Results: The mean time interval between the 2 ⁶⁸Ga-DOTATATE studies was 9.6 ± 7.2 mo, and the mean time gap between the last Sandostatin LAR injection and the second ⁶⁸Ga-DOTATATE study was 25.1 ± 14.8 d. The pretreatment mean SUV_max and SUV_mean were both significantly higher in the thyroid, liver, and spleen (P < 0.05) than the values measured after the administration of Sandostatin LAR. No significant differences were found among the uptake indices for residual primary tumor or any metastatic lesions in the liver, bone, lung, or lymph nodes before and after Sandostatin LAR administration (P > 0.05). Conclusion: Long-acting octreotide treatment diminished ⁶⁸Ga-DOTATATE uptake in the liver, spleen, and thyroid but did not compromise tracer uptake in residual primary tumor and metastatic lesions. These findings have a direct impact on the interpretation of ⁶⁸Ga-DOTATATE PET/CT scans.

Clinical Applications of Small-molecule PET Radiotracers: Current Progress and Future Outlook

Radiotracers, or radiopharmaceuticals, are bioactive molecules tagged with a radionuclide used for diagnostic imaging or radiotherapy and, when a positron-emitting radionuclide is chosen, the radiotracers are used for PET imaging. The development of novel PET radiotracers in many ways parallels the development of new pharmaceuticals, and small molecules dominate research and development pipelines in both disciplines. The 4 decades since the introduction of [¹⁸F]FDG have seen the development of many small molecule PET radiotracers. Ten have been approved by the US Food and Drug Administration as of 2016, whereas hundreds more are being evaluated clinically. These radiotracers are being used in personalized medicine and to support drug discovery programs where they are greatly improving our understanding of and ability to treat diseases across many areas of medicine including neuroscience, cardiovascular medicine, and oncology.

A case of added value of 123I-mIBG SPECT/CT imaging in the diagnosis of a pheochromocytoma extending into the left adrenal vein

We present the case of a 48-year-old patient with a left adrenal incidentaloma found on computed tomography (CT) for which the diagnosis of pheochromocytoma was confirmed by a 24-hour urinary dosage of norepinephrine. The ¹²³I-mIBG scintigraphy showed a high uptake of ¹²³I-mIBG in the left adrenal gland and, additionally, the single photon emission computed tomography combined with a low-dose CT (SPECT/CT) suggested the extension into the adrenal vein. The diagnostic CT and magnetic resonance images agreed with these findings and the subsequent surgery confirmed the vascular invasion.

Update on Modern Management of Pheochromocytoma and Paraganglioma

Despite all technical progress in modern diagnostic methods and treatment modalities of pheochromocytoma/paraganglioma, early consideration of the presence of these tumors remains the pivotal link towards the best possible outcome for patients. A timely diagnosis and proper treatment can prevent the wide variety of potentially catastrophic cardiovascular complications. Modern biochemical testing should include tests that offer the best available diagnostic performance, measurements of metanephrines and 3-methoxytyramine in plasma or urine. To minimize false-positive test results particular attention should be paid to pre-analytical sampling conditions. In addition to anatomical imaging by computed tomography (CT) or magnetic resonance imaging, new promising functional imaging modalities of photon emission tomography/CT using with somatostatin analogues such as ⁶⁸Ga-DOTATATE (⁶⁸Ga-labeled DOTA(0)-Tyr(3)-octreotide) will probably replace ¹²³I-MIBG (iodine-123-metaiodobenzylguanidine) in the near future. As nearly half of all pheochromocytoma patients harbor a mutation in one of the 14 tumor susceptibility genes, genetic testing and counseling should at least be considered in all patients with a proven tumor. Post-surgical annual follow-up of patients by measurements of plasma or urinary metanephrines should last for at least 10 years for timely detection of recurrent or metastatic disease. Patients with a high risk for recurrence or metastatic disease (paraganglioma, young age, multiple or large tumors, genetic background) should be followed up lifelong.

Endocrine Tumors Causing Arterial Hypertension: Pathophysiological Mechanisms and Clinical Implications

Some tumors are a relatively rare and amendable cause of hypertension, often associated with a higher cardiovascular morbidity and mortality, as compared with that of both general population and patients with essential hypertension. This worse prognosis is not entirely related to blood pressure increase, because the release of substances from the tumor can directly influence blood pressure behavior. Diagnostic approach is challenging and needs a deep knowledge of the different neuro-hormonal and genetic mechanisms determining blood pressure increase. Surgical tumor removal can, but not always, cause blood pressure normalization, depending on how early was tumor detection, since a long-standing history of hypertension is often associated with a much weaker effect on blood pressure. Moreover, target organ damage can be affected by the substances themselves released by the tumors as well as by tumor removal. In this review we consider the phenotype and genetic features of patients with tumor-induced hypertension and focus on their diagnostic work-up.

Metabologenomics of Phaeochromocytoma and Paraganglioma: An Integrated Approach for Personalised Biochemical and Genetic Testing

The tremendous advances over the past two decades in both clinical genetics and biochemical testing of chromaffin cell tumours have led to new considerations about how these aspects of laboratory medicine can be integrated to improve diagnosis and management of affected patients. With germline mutations in 15 genes now identified to be responsible for over a third of all cases of phaeochromocytomas and paragangliomas, these tumours are recognised to have one of the richest hereditary backgrounds among all neoplasms. Depending on the mutation, tumours show distinct differences in metabolic pathways that relate to or even directly impact clinical presentation. At the same time, there has been improved understanding about how catecholamines are synthesised, stored, secreted and metabolised by chromaffin cell tumours. Although the tumours may not always secrete catecholamines it has become clear that almost all continuously produce and metabolise catecholamines. This has not only fuelled changes in laboratory medicine, but has also assisted in recognition of genotype-biochemical phenotype relationships important for diagnostics and clinical care. In particular, differences in catecholamine and energy pathway metabolomes can guide genetic testing, assist with test interpretation and provide predictions about the nature, behaviour and imaging characteristics of the tumours. Conversely, results of genetic testing are important for guiding how routine biochemical testing should be employed and interpreted in surveillance programmes for at-risk patients. In these ways there are emerging needs for modern laboratory medicine to seamlessly integrate biochemical and genetic testing into the diagnosis and management of patients with chromaffin cell tumours.

Leptomeningeal dissemination of a low-grade lumbar paraganglioma: case report

Leptomeningeal dissemination of paraganglioma is rare, with only 2 prior cases in the literature. The authors present the case of a metastatic low-grade lumbar paraganglioma via leptomeningeal dissemination. This report emphasizes the utility of 3,4-dihydroxy-6-¹⁸F-fluoro-l-phenylalanine (¹⁸F-FDOPA) PET scanning for diagnosis, as well as the combination of radiation therapy and alkylating chemotherapeutic agents for the treatment of this rare phenomenon. The patient was a 61-year-old woman who presented with low-back pain and was found to have an isolated L-3 intrathecal tumor on MRI. Sixteen months after gross-total en bloc resection of the paraganglioma, the patient again became symptomatic with new neurological symptoms. MRI findings revealed enhancing leptomeningeal nodules throughout the spine. ¹⁸F-FDOPA PET/CT scanning was used to confirm the diagnosis of disseminated paraganglioma. Intrathecal thiotepa, radiation therapy, and systemic therapy with capecitabine and temozolomide have been used sequentially over a 2-year period, with each able to stabilize tumor growth for several months. The authors also summarize the 2 other reports of leptomeningeal dissemination of paragangliomas in the literature and compare the course and management of the 3 cases.

Morphological and functional imaging of neck paragangliomas

OBJECTIVE

To review the optimal techniques for localization and characterization of neck paragangliomas (PGL).

MATERIAL AND METHODS

Systematic review of the literature from the PubMed/Medline database.

RESULTS

Neck PGL are hypervascular tumours essentially arising from paraganglionic tissue situated at the carotid bifurcation (carotid body) and along the vagus nerve. Morphological and functional imaging are indicated to confirm the diagnosis, identify multifocal disease and for local and regional staging. MR angiography is the noninvasive technique of choice. CT scan and especially CT angiography are excellent alternatives for diagnosis and staging. Conventional arteriography remains useful preoperatively for embolization and occlusion tests. Functional imaging allows localization and characterization of PGLs. Somatostatin receptor scintigraphy (SRS) was the reference imaging technique for staging of sporadic PGLs. The indications for PET imaging have been extended over recent years in parallel with the development of new tracers such as [¹⁸F]-FDOPA PET or ⁶⁸Gallium-labelled DOTA peptides. ⁶⁸Gallium-labelled DOTA peptides has become the first-line imaging modality in the evaluation of cervical PGLs, regardless of the genetic background.

CONCLUSION

Morphological and functional imaging is essential for the staging of neck PGL.

Endocrine tumors associated with the vagus nerve

The vagus nerve (cranial nerve X) is the main nerve of the parasympathetic division of the autonomic nervous system. Vagal paragangliomas (VPGLs) are a prime example of an endocrine tumor associated with the vagus nerve. This rare, neural crest tumor constitutes the second most common site of hereditary head and neck paragangliomas (HNPGLs), most often in relation to mutations in the succinate dehydrogenase complex subunit D (SDHD) gene. The treatment paradigm for VPGL has progressively shifted from surgery to abstention or therapeutic radiation with curative-like outcomes. Parathyroid tissue and parathyroid adenoma can also be found in close association with the vagus nerve in intra or paravagal situations. Vagal parathyroid adenoma can be identified with preoperative imaging or suspected intraoperatively by experienced surgeons. Vagal parathyroid adenomas located in the neck or superior mediastinum can be removed via initial cervicotomy, while those located in the aortopulmonary window require a thoracic approach. This review particularly emphasizes the embryology, molecular genetics, and modern imaging of these tumors.